Citing the high risk of a devastating fire in the Mount Tamalpais watershed, the Marin County Civil Grand Jury issued a report Monday advocating limited use of herbicides to control the spread of French broom.

The report comes as the Marin Municipal Water District is preparing an environmental impact report on a vegetation management plan that contains two options. One approach calls for manual removal of broom; the other would combine manual efforts and the controlled use of herbicides, including glyphosate, the active ingredient in Roundup. The district has estimated the manual approach would cost $5.6 million a year, while the method that employs the herbicide would cost $1.6 million.

In its new report, the grand jury said it "strongly believes that the high risk of wildfires far exceeds the very low risk associated with the controlled use of herbicides." The grand jury recommended the water district board approve the herbicide option, concluding it is "the only reasonable alternative to control the Broom infestation within the watershed."

The watershed supplies drinking water to much of Marin with the exception of Novato and parts of West Marin. It consists of 18,900 acres and borders 11 communities: Mill Valley, San Anselmo, Ross, Kentfield, Fairfax, Larkspur, Corte Madera, Woodacre, Lagunitas, Forest Knolls and San Geronimo. Those communities account for 13,200 structures within one mile of the watershed boundary.

"These 13,200 structures are in imminent danger of a devastating wildfire similar to the 1991 Oakland Hills firestorm, which destroyed 2,900 structures and killed 25 people," the grand jury said. "The watershed is rated high for fire risk by the California Department of Forestry."

The water district used glyphosate to attack the non-native, invasive broom for three years until August 2005; but then the district's Board of Directors imposed a moratorium on the use of herbicides after complaints from residents concerned about potential health impacts if the chemical leached into reservoirs. Broom infests more than 1,200 acres of the watershed and it is spreading at a rate of at least 30 acres per year.

Non-chemical approaches to controlling broom — hand pulling or mechanical grubbing, burning and goat grazing — have proved ineffective, the grand jury said. "The underground root stalks and millions of seeds released by the seedpods proved to be overwhelming."

In addition to glyphosate, options under consideration by the water district include the possible use of conventional herbicides — Aquamaster, Gallon 4 Ultra Triclopyr and Transline — as well as surfactants, compounds such as Competitor and Sylgard 309.

As one of its major findings, the grand jury wrote, "Current scientific studies indicate that the recommended application of glyphosate with surfactant approved for use within watershed areas pose no significant risk."

Glyphosate-based herbicides have been certified as safe by the Environmental Protection Agency and are used by the Marin County Parks and Open Space District and on federal, county and state lands, the grand jury noted.

But Debbie Friedman of Mill Valley, co-founder of Moms Advocating Sustainability, said, "It's hard to understand how they came to that conclusion when the science has been unfolding for years and continues to come forward with information about just how dangerous these herbicides are."

"We understand that the water district is dealing with a host of issues, including biodiversity issues and fire danger," Friedman added. "However, public health must continue to be the number one priority."

Frank Egger, a Ross Valley Sanitary District board member and former Fairfax mayor who has tracked the issue, had a similar reaction to the report.

"The grand jury says the EPA has said that glyphosates are safe. It's never said that," Egger said. "In fact, there is testing going on right now. Monsanto will tell you that glyphosates are safe."

Egger also cast doubt on the water district's cost estimate of $5.6 million per year for controlling broom manually.

"They have never shown how it adds up to $5.6 million," Egger said. "The town of Fairfax runs its entire budget on $6 million a year and that includes 30 employees."

Libby Pischel, water district spokeswoman, responded, "It's a valid number based on what we know."

One table in the plan's appendix lists a $30-per-hour labor rate for manual extraction of broom and a labor cost per acre of $4,556.

Fairfax Councilman Larry Bragman also questioned the $5.6 million estimate.

"That number includes eradication of broom from all five of the district's zones," Bragman said, even though the plan calls for only limiting spread in several of the smaller, more infested zones. Bragman said the district should consider collecting a fee from ratepayers for maintenance of watershed lands.

"Maybe it is time that we recognize the value that is there," he said, "and impose a modest fee to take care of it."